1. Field of Invention
The present invention relates to a counterweight mechanism for a pressure relief door which may be used in a filterhouse of a gas turbine intake system.
2. Discussion of Prior Art
The use of a counterweight mechanism on a pressure relief door is known. In a gas turbine intake system, an associated filterhouse conventionally has a pressure relief door. A pressure relief door can be provided as a blow-in door for a filterhouse. Such a blow-in door opens when the pressure inside the filterhouse goes lower than a specified amount below the surrounding ambient atmospheric pressure (i.e., a specified pressure differential is exceeded). Exceeding the specified pressure differential can occur due to a variety of reasons, such as blockage of the filtration media. Opening the door (e.g., a blow-in door) may help to protect the intake system from damage. In addition, opening the door can help maintain sufficient airflow to the turbine and possibly avoid or delay the need for a shutdown.
In order to maintain the door in a closed condition prior to experiencing a pressure differential exceeding the specified pressure differential, it is known to fixedly attach a counterweight to the door. Prior to opening, the door is held closed by a moment force that results from the weight of counterweight acting about the pivot axis of the door. The closing moment force (Mclosing) is calculated as follows:Mclosing=W·X where W is the weight, of the counterweight and X is the horizontal distance from the counterweight to the pivot axis of the door. The difference between the pressure outside the filterhouse and the pressure inside the filterhouse creates an opening force upon the door. When the opening force is greater than the closing moment force, the door pivots open.
However, there are several shortfalls with existing counterweight mechanisms. A first shortfall noted by the inventors is that as the door opens, the horizontal distance (X within the moment force equation) of the counterweight from the pivot axis decreases. Consequently, the closing moment force decreases once the door begins to move from a fully closed position. It has also been noted that, simultaneously, the opening force decreases as the pressure drop is relieved by the movement of the door from its fully closed position. The combination of these factors may cause the door to vibrate or “flutter” movement as it hunts in an effort to achieve equilibrium. Still further, it has been noted that the door will naturally tend to continue to move freely because the door may not have external damping and may possess a high level of inertia. Unfortunately, some operators may weld the pressure relief door shut to prevent such flutter.
Moreover, some existing counterweights are attached to the door at the side of the door within the filterhouse. If the counterweight needs to be serviced or adjusted, the gas turbine may need to be shut down for workers to gain access to the counterweight located within the filterhouse. Such turbine shutdown may be economically costly. Also, servicing the counterweight within the filter housing may involve a need for workers to access the clear air path. This may add further complication, such as the need to acquire applicable permits and the potential for contamination. Furthermore, there may be other issues associated with counterweight components that may become loose if the location of the counterweight is within the filter housing.
Thus, there is need for improvements to address such issues.